How do I solve 2 down in Daily Telegraph Cryptic 31243?

Question

Accepted Answer

2 down reads "Vital ship in an entrepot, finally" (9 letters); the answer is IMPORTANT. It's a letter-selection clue: take specific letters from a longer source. 'First of' means the opening letter, 'extremely' means first + last, 'regularly' means every other letter, 'oddly' / 'evenly' means odd or even positions. The full step-by-step breakdown is on this page.

Vital ship in an entrepot, finally (9)

2D — Vital ship in an entrepot, finally (9) — IMPORTANT